Researchers studying the Greenland ice sheet know they're working with "a clock that is ticking," says Marco Tedesco, a scientist with the National Science Foundation whose most recent visit there shed new light on how quickly the Arctic island nation's ice is melting and the impact it could have on global sea level rise.

"Everybody is trying to put out the best research in the shortest time ... for the scientific community to move at a faster pace."

Tedesco was part of a research mission earlier this summer that captured first-ever footage of meltwater draining from the huge lakes that form on top of the Greenland ice sheet every summer, when warmer temperatures melt the ice and snow that accumulates on the surface.

Because of the extreme pressure the melted surface water puts on the ice -- it can pool into lakes that can stretch a few miles across and nearly 20 feet deep -- cracks form, allowing the surface water to drain all the way through the ice and down to the bedrock in many cases.

"It was like when you pull the plug on a tub," Tedesco said of the scene he and his colleagues filmed in June and July. "We could see these huge blocks of ice, a few meters wide and a few meters high, swirling around on the surface of the lake while it was draining."

Once it reaches the bottom, the water acts as a lubricant underneath the massive ice sheet, he added. "It's like the ice starts floating for a little bit -- it's a little bit buoyant on the bedrock."

Greenland's annual melting has picked up speed over the past decade, setting a new record in 2012 when an estimated 97 percent of the ice sheet experienced some degree of melting.

The measurements Tedesco and his team took of the melting this summer have major potential implications for how scientists understand how quickly the ice sheet is losing its mass (estimated at about 680,000 cubic miles of ice), which it sheds in two ways: surface water runoff into the ocean, and from huge chunks of ice that break off and float away on the sea.

"You can imagine these like a river of ice that is dumping material into the ocean," he explained. "Those two processes are not disconnected. It’s not that you are changing one thing on the surface and that stays on the surface -- changing the melting on the surface of the ice sheet has a very strong potential to change the entire behavior of the ice sheet."

In contrast with Arctic sea ice -- which some scientists expect will disappear completely in the summer by the middle of this century -- the Greenland ice sheet isn't in danger of melting completely away "for thousands of years," Tedesco said. That shouldn't provide any comfort, he adds.

"Even though Greenland holds the potential for 6 or 7 meters (about 19 to 21 feet) of sea level rise, you don't need all that to make a disaster," he added, noting that even a few inches to a foot of sea level rise can make a major difference in cities like New York when major hurricanes strike.

"The acceleration of the melting of Greenland can impact things far away from Greenland, and it can change things around Greenland itself," he said, by discharging massive amounts of freshwater into the oceans, which would have a major impact on fishing operations in nearby seas. It might also mean that many more icebergs could begin breaking off the island and floating into the ocean, where they could sail as far away as the coasts of the U.S. and Canada.

"All of these factors are potentially a consequence of the melting in Greenland."